The present invention relates to a method of producing a semiconductor device. More specifically, the present invention relates to a method of producing a semiconductor device such as a high voltage power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) formed on a silicon carbide substrate.
Conventionally, when a semiconductor device is formed on a silicon carbide substrate, first, a silicon carbide layer is formed on a seed substrate formed of silicon carbide with an epitaxial growth method, thereby preparing a silicon carbide substrate. Then, an N-type impurity is diffused in the silicon carbide substrate at a lower concentration to form an N drift diffusion layer.
In the next step, a resist mask is formed on the N drift diffusion layer through photolithography for exposing a forming area of a P well layer. After a P-type impurity formed of aluminum is implanted at a lower concentration to form a P low concentration implantation layer, a carbon film is formed to cover an upper surface of the silicon carbonate substrate to prevent an undulation called step bunching from forming.
In the next step, the P low concentration implantation layer is activated through a thermal processing at a high temperature higher than 1,600° C. to form the P well layer. When an MOSFET is formed, the upper surface of the silicon carbide substrate is thermally oxidized to form a gate oxidation film after the carbon film is removed (refer to Patent Reference).
Patent Reference: Japanese Patent Publication No. 2005-353771
The step bunching is an undulation formed on a surface through evaporation of silicon between crystal lattices when the silicon carbide substrate is exposed at a high temperature higher than 1,600° C., i.e., a specific phenomenon of a method in which a silicon carbide substrate with high temperature resistance is used.
In the conventional method, when the gate oxidation film of the MOSFET is formed, a thermal oxidation film is formed with the thermal oxidation method. Accordingly, when the thermal oxidation film is formed on the silicon carbide substrate normally required for a processing temperature higher than 1,600° C., the step bunching tends to be formed in an interface between the gate oxidation film formed of silicon oxide through the thermal oxidation and the silicon carbide substrate.
When the step bunching is formed, mobility of charges in a channel region decreases. Accordingly, a channel resistivity increases, thereby lowering an element characteristic of the semiconductor device.
In view of the problems described above, an object of the present invention is to provide a method of producing a semiconductor device capable of solving the problems of the conventional semiconductor device and the conventional method of producing the semiconductor device.
In the method of producing a semiconductor device of the present invention, it is possible to form a gate oxidation film formed of a thermal oxidation film on a silicon carbide substrate while maintaining flatness of an interface between the gate oxidation film and the silicon carbide substrate.
Further objects and advantages of the invention will be apparent from the following description of the invention.